This invention relates to improvements in or to the construction of a heater unit for use in air conditioning systems for automotive vehicles.
Air conditioning systems for automotive vehicles in general include a type which comprises a cooler unit and a heater unit which are fabricated separately from each other, wherein air which is cooled by the operation of an evaporator arranged within the cooler unit or air which is supplied in a non-cooled state when the evaporator is at rest (outside air or inside or recirculated air) is introduced into the heater unit through an air inlet where it is heated by a heater core provided within the heater unit and then discharged through an upper or face air outlet or a floor air outlet both formed in the casing of the heater unit and then through a duct.
In such a heater unit, to obtain a desired discharge air temperature, the discharge air temperature is controlled by changing the angular position of an air-mix damper provided on the heater or in the vicinity thereof so as to change the mixture ratio of warm air passing through the heater core and cold air bypassing the heater core.
A conventional heater unit in general comprises a casing formed with an air inlet and various air outlets, a heater core disposed in the vicinity of the air inlet in such an arrangement that one side surface of the heater core cooperates with an inner wall surface of the casing to define a cold air passage therebetween, whereby air is guided to the upper side of the heater core and then downwardly flows through it, and an air-mix damper located within the cold air passage and pivoted at a point on the heater core for controlling the amount of air which is introduced into the heater core through the cold air passage. Warm air passing through the heater core and cold air passing through the cold air passage, i.e., bypassing the heater core can be mixed with each other in a zone downstream of the heater core.
The heater unit having the above-mentioned construction, however, has drawbacks that the cold air passage is inevitably small in space, resulting in large air flow resistance produced in the cold air passage, which leads to discharge of cold air into the passenger compartment at a limited flow rate, the presence of the air-mix damper within the cold air passage causes a substantial decrease in the space of the cold air passage, which further increases the air flow resistance in the passage, and the maximum pivotable angle range of the air-mix damper is so small that pivoting of the air-mix damper through a certain angle causes an abrupt and large change in the mixture ratio of cold air to warm air, thus making it difficult to carry out accurate and fine temperature control.